Genic Type-Genetic basis of Sex Determination
In some organisms, certain indepe~ident genes located on different chromosomes are responsible for sex determination. Most species of fish illustrate this mode. The male may be represented as AA' for the sex determining genes, and the female as AA (as shown in figure). According to this assumption, maleness is determined by the genc A' which is dominant over A.In a parasitic wasp, called Habrobracon, genes are responsible for sex determination in a different way. The sex determining gene has multiple alleles (Xu, Xb, XC,Xd).When two alleles in a zygote are different or hcterozygous (XaXb, XaXc, X"XC, etc.) a normal, fertile female is formed. If the alleles in the zygote are in homozygous (XaXa, XbXb, etc.) or hemizygous (Xa,Xb,Xc, etc.) condition males are formed.